The invention relates to a dispensing device and method for dispensing fluid materials including liquids and pastes, especially for use with liquid gasketing materials, particularly for the automotive industry.
Anaerobic adhesives are used widely in industry for many applications. One particular application is the use of such adhesives as sealants in the provision of gaskets on flanges for use in the combination of parts in the automotive industry. Traditionally, there are two ways to apply a liquid gasketing material in the automotive industry, robotic application or screen printing. Robotic application includes the incorporation of a nozzle onto a programmed automated arm which then moves the nozzle about a substrate in a predetermined manner. Robotic applicators have the advantage over screen printing that as the adhesive is dispensed directly from a single nozzle to the substrate, there is no large surface of adhesive which results in the applicator being more flexible and cleaner. In comparison, as screen printing involves placing a screen over the substrate it only requires the same amount of time for the application of adhesive regardless of the complexity of the dispensed pattern geometry. As a result of advantages of robotic application, there has been a trend towards robotic dispensing but it is desirable to improve the speed and quality of application in such dispensing.
The conventional dispensing equipment uses a needle which is usually positioned 2-3 mm above the substrate to which the adhesive is to be applied. Desirably the substrate is presented at the same height each time, such that the adhesive is applied to a substantially planar substrate. The substrate is desirably mated with stops to ensure consistent substrate height. However, this is not always possible.
In the provision of liquid gasketing materials it is common to use anaerobic adhesives. These adhesives are so called because they do not cure in the presence of air. As such the adhesives are typically supplied in mechanically sealed permeable containers with air contained therein The nature of the constituents of the adhesive, and the fact that it is the absence of air that facilitates curing means it is essential for the adhesive to contact air during storage and prior to application. Otherwise, the shelf life of the adhesive becomes compromised.
As such, it is not uncommon for these products have air bubbles contained therein. The presence of the air bubbles in the adhesive tends to cause breaks in the flow from the container. After the passage of a bubble out of the dispensing tip, normal adhesive is dispensed again, which re-establishes the continuity of the adhesive bead. The height of the nozzle from the substrate and the speed of the robotic dispensing arm affect the quality of adhesive bead being dispensed. If a break occurs and the nozzle is at a large distance away from the substrate then the length of the break as seen on the substrate will be large; similarly it will be understood that the greater the nozzle speed, the larger the break on the substrate.
In commercial application of adhesives to form gaskets on flanges it is not always possible to present the flange substrate to the dispensing nozzle in a consistent planar manner. In such situations the substrate can be presented at varying heights and angles to the robotic dispensing arm. Although it is possible to program the robot to accurately manoeuvre around obstacles on a well presented flange, it is difficult to compensate for fluctuations arising from a badly presented flange. The inability of the robotic dispensing arm to compensate for such fluctuation may result in poorly-applied gasketing materials.
In common applications the smallest adhesive beads that should be dispensed are of approximately 2 g/m2, which is recommended in industry practice to be achieved using a nozzle having a port diameter of 0.8 mm. This preferred port diameter is calculated from a relationship that exists between the cross sectional area of the nozzle port and velocity of fluid product exiting said port and the area of the dispensed bead on the substrate and the velocity of the robot arm. To ensure that an adequate area of adhesive is dispensed using predetermined recommended relationships between the robot and product speed it is calculated that a port diameter of 0.8 mm is sufficient. Depending on the viscosity of the adhesive, the dispensed adhesive bead may be dispensed in a generally semi-circular/circular section on the substrate. It is preferable to achieve the adhesive velocity in the nozzle of approximately twice that of the robotic dispensing arm speed. This minimises the effect of air bubbles entrained in the adhesive. Depending on the application one can tolerate a break of up to about 16 mm in the dispensed bead of adhesive as the adhesive will flow when the substrates are brought together. In the range of about 16-22 mm one observes necking, which although it will heal itself, may form a gasket which is not constant across the width of the substrate. At a gap greater than about 22 mm one may observe a complete break, which results in an incomplete seal when the substrates are brought together and the joint may leak and will either have to be reassembled or repaired.
When the adhesive is applied as a gasketing material to a flange, it is common to use vision inspection systems to ensure quality of application of the adhesive bead, especially when considering the cost of visual inspection as opposed to the cost of reassembly or repair resulting from poorly applied gasketing material. If the vision inspection systems detect any break in the applied bead it is common practice to manually apply additional adhesive at the point of breakage. Additional tests that may be incorporated include the xe2x80x9cblow-outxe2x80x9d test, which involves the integrity testing of two mated and thereby sealed flanges. After complete assembly the unit is pressurised to approximately xc2xd bar, the ability of the unit to maintain the pressure being indicative of an adequate seal.
There have been proposals to alter the adhesive product so as to minimise the possibility of breaks occurring in the dispensed bead. This may be achieved by reducing the amount of air within the adhesive product, however, as noted, this comes with a cost of a reduction of shelf life. By refrigeration it is possible to counteract the shelf life reduction somewhat but even so the shortened shelf-life is an added expense and results in problems for manufacturers. Accordingly, it would be desirable to provide a dispensing system which allows for a bead of a liquid product to be applied to a surface with little to no interruption in the bead from air entrained in the liquid product.
The present invention provides a dispensing device and a process for using said device which allows for the application of high quality beading, in particular in the application of anaerobic adhesives or sealants to form gaskets. The invention is also applicable to other fluid dispensable materials.
In one aspect the invention provides a device suitable for the dispensing of a fluid dispensable material in ribbon form to a substrate. The device includes
at least one dispensing nozzle having at least one inner conduit leading to an exit port and adaptable to be in fluid communication with a supply source for the fluid dispensable material, the nozzle having an end portion defining the exit port such that a ribbon of fluid dispensable material can be applied to the substrate, and
means for mounting the nozzle for substantially perpendicular free movement relative to the substrate such that the end portion of the nozzle maintains contact with the fluid material applied to the substrate, movement towards the substrate being effected by an applied force and movement away from the substrate being effected by a thrust exerted by the dispensed fluid material against said end portion of the nozzle and the dispensable material in the exit port.
The invention also provides an apparatus for dispensing a fluid product onto a substrate, the apparatus comprising a nozzle and means for mounting the nozzle with at least one degree of freedom allowing movement of the nozzle relative to the substrate with movement towards the substrate being effected by a substantially constant force and movement away from the substrate being effected by a force related to the pressure exerted by the dispensed fluid on the nozzle.
The invention also provides a method for dispensing a fluid dispensable material to a substrate comprising the steps of
mounting a dispensing nozzle in a manner which allows substantially perpendicular free movement of the nozzle relative to the substrate,
facilitating the application of an applied force on the dispensing nozzle to effect movement of the nozzle in a direction towards the substrate,
supplying the fluid dispensable material to an exit port which is defined by an end portion of the nozzle, applying the material to the substrate, and controlling the applied force in relation to a thrust exerted by the dispensed fluid material on the end portion of the nozzle and the dispensable material therein such that the end portion of the nozzle maintains contact with the dispensed material applied to the substrate.